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Measuring Mast Rake

Posted By: tback

Measuring Mast Rake - 07/05/06 05:42 PM

Moving this discussion from "First Pics".

Quote
First trap measurement = hounds to bow tang. Set the trap at that (add some line if you need to)
Second trap measurement = First trap measurement moved aft to where it touches the deck. This is hounds to deck aft measurement and is equal to hounds to bow tang at foredeck measurement.


To be sure, you measure physically to the tang (bow), then to the center hull (aft); ie the aft measurement might be to the center of the deck hole (not from center hull forward to center hull aft -- which is okay if we keep consistent but does result with slightly different calculations).

When we compare numbers should we measure from the rear beam centerline? Might be easier and more accurate to measure from the aft-most part of the aluminum beam.
Posted By: bobcat

Re: Measuring Mast Rake - 07/05/06 07:22 PM

I would think that the declarer would state his landmark.
He could be so much in front, so much behind, so much below transom etc. I have assumed that the edge was the reference point. Only when measuring a point on the beam would centerline be mentioned.
Posted By: Jamie

Re: Measuring Mast Rake - 07/06/06 03:30 AM

It's my belief, the greater distance from the two measurements, assuming it doesn't exceed 90 degrees, the more accurate the measurement. So I suspect, going from bow topside tip to middle topside stern would give you the most accurate measurement for a single style of boat. Haven't pulled out the calculator to confirm this, but just seems right.
Posted By: Jalani

Re: Measuring Mast Rake - 07/06/06 06:41 AM

You're probably right, but given that most of us sail with some kind of aft rake, past efforts have shown on almost all classes that if you go from the tip of the bow, the aft measurement ends up behind the boat - not a lot of use! <img src="http://www.catsailor.com/forums/images/graemlins/frown.gif" alt="" />

Therefore cat sailors have established this 'protocol' that the forward trap measurement is always taken at EITHER the bow tang or at the deck above the bow tang in the case of boats with lowered tangs.
Posted By: bobcat

Re: Measuring Mast Rake - 07/06/06 04:12 PM

Ok boys, time to start talking numbers. I would like to start out but the computer is 60 miles from the boat.

With the intent of being to edit this later, I will now state that when I hold my forward trapeze line, after suitably extending it, to where the bow tang meets the hull, I find that my aft measurement is XX inches down the transom.

If I'm real keen, I will try to get some photo's to illustrate the thread with.
Posted By: Wouter

Re: Measuring Mast Rake - 07/06/06 06:36 PM



I always use the top of the deck next to the bridle tangs, not the tangs themselfs. Then I measure where the line touches to top of the deck on the rear.

Wouter
Posted By: tback

Re: Measuring Mast Rake - 07/06/06 07:22 PM

I won't be able to take measurements until Gilligan's Run July 22.
Posted By: pdwarren

Re: Measuring Mast Rake - 07/09/06 09:27 PM

Did mine today: from the deck above the tang to the outer edge of the deck at the stern. I'm on the front edge of the rear beam. This is one hole more upright that I've sailed with up to this point - I'll let you know how it goes.

Paul
Posted By: bobcat

Re: Measuring Mast Rake - 07/10/06 02:12 PM

So I have lost the ability to edit my previous post.
I measured and arrived at 3 inches down the transom. Looking at the picture I realize that I should have been closer to the pintles. But the idea is presented here. It's been a week and I haven't heard from VM on the concept that I can't rake forward enough.
[Linked Image]

Attached picture 80372-IMG_0398.JPG
Posted By: bobcat

Re: Measuring Mast Rake - 07/10/06 02:16 PM

This is a pic of what I feel is extreme rake. Compare the mast to the flagpole and masts in the background. Strangely, I have not been aware of strong weather helm. The helm is so light that I'm not aware of a tug at all. It could be weather helming, it is just that it hasn't forced itself into my conciousness by needing two hands.
[Linked Image]

Attached picture 80373-IMG_0395.JPG
Posted By: pdwarren

Re: Measuring Mast Rake - 07/10/06 02:38 PM

Quote
Strangely, I have not been aware of strong weather helm. The helm is so light that I'm not aware of a tug at all. It could be weather helming, it is just that it hasn't forced itself into my conciousness by needing two hands.


The other possibility is that your rudders are raked forward and that's concealing any weather helm.

Was your measurement from the tang, or from the deck above the tang? Not that that makes a huge difference (probably less than an inch).

In any event, it seems that my forestay is a little bit shorter than yours (presumably this is a European vs US thing).

Paul
Posted By: bobcat

Re: Measuring Mast Rake - 07/10/06 03:14 PM

It was from the deck above the tang.

The rudder rake thing is something I haven't investigated. As far as I know, it isn't adjustable. I have the rope-based surf system and just pull them down and lock them.

Yesterday, I caught a race with winds in the high-mid teens (knots). Nice single-trapped ride, only a little extra downhaul pulled on. Downwind under spi was a bit intimidating. I am still avoiding trapezing and have yet to learn my angles. I gybed onto port way too late and the high reach scared me fierce. So I bore off deep for a while, doused it and sailed back to the mark on main alone. Certainly had lee-helm but only noticed it if I tried to put the stick down.
Posted By: Robi

Re: Measuring Mast Rake - 07/10/06 03:38 PM

Actually Bruce, your image looks about right compared to the ammount of rake I run. My mast leans pretty far back as well.

I am going to start sailing with my mast rake one point further foward.

As far as adjusting your rudders, the only way I think its posible for us, is by using plastic shims inside the rudder stocks.
Posted By: Wouter

Re: Measuring Mast Rake - 07/10/06 03:45 PM



Well I think we can conclude here that at least the rudders are perfectly balanced. Not unimportant I say.

I personaly FEEL that your rake it too much, 3 inches DOWN on the transom is alot, but I have no hard data to support that. I feel the line should touch the deck somewhere between the rearbeam and transom. Maybe we can have a sound-off with everybody giving their measurements ?

When I received the ordered stays for my boat I found the supplier misread the distances I gave him as well. But mine issue was the other way around. May mast was almost leaning forward. My forestay proved to be 130 mm to short and my sidestays were 70 mm to long. I made the forestay longer by looping a 4 mm lines several times through the eyes (I still use that same line) and I had my sidestays shortened by local chandler (while I was watching and checking) by having the old terminal cut off and a new terminal fitted. Now I'm all right.

How low are you on the forestay adjuster ?

How high are you on the sidestay adjusters ?


Quote

So I bore off deep for a while, doused it and sailed back to the mark on main alone. Certainly had lee-helm but only noticed it if I tried to put the stick down.


When confronted with this again, it is best to continue sailing optimal angles in the way of speed, then drop the spi and reach for the mark.

If you can make the mark by just pointing a little higher without collapsing or letting go of the kite then that is most efficient but when you CAN'T then the above approach is better, also in the way of time spend getting to the mark. Trying to do it both way simultaniously is NOT best.

Wouter
Posted By: bobcat

Re: Measuring Mast Rake - 07/10/06 04:17 PM

Quote

How low are you on the forestay adjuster ?

How high are you on the sidestay adjusters ?

Wouter


I only have 1 hole left to me on the forestay for more forward rake.
On the sidestay StayMasters I am currently at 8.5 where 10 is the longest.
Posted By: tshan

Re: Measuring Mast Rake - 07/10/06 06:38 PM

I think it looks fairly dramatic. I'll try to measure my set up this weekend and forward it on for comparison.
Posted By: Wouter

Re: Measuring Mast Rake - 07/10/06 10:38 PM



I checked the settings of one EU Blade F16 just now. Using the method describe with top of deck variation, it touched the rear egde of the inspection hatch. It still looks like a considerable amount of rake but less then yours. Boat felt well balanced to me when I sailed it and the owners are getting faster and faster..

My own boat (modified Taipan) has now very little mast rake. The mast is almost straight up, I'm well ahead of the rearbeam when measuring. Uni-rigged it handles very well that way. I changed it at the beginning of this season. Haven't done to much sloop sailing yet this season and it may be a little too much forward for that. But I will know after this weekend I guess.

Wouter
Posted By: Robi

Re: Measuring Mast Rake - 07/11/06 01:08 AM

I cant wait to get mine measured up!!! I am sure I am close to what Bruce (UNICAN - Bobcat) is running. I remember by looking at the boat. Plus I am at usually between 2 and 1 on my chainplates.
Posted By: tback

Re: Measuring Mast Rake - 07/23/06 09:28 PM

okay, measured my mast rake at Gilligans Run.

My previous rake produced significant weatherhelm. After measuring I can understand why.

Measured from the Bridle Tang (center top of hull) then pulled back to centerline of rearhull, my measurement went down the aft transom about 2". This setting was with the forestay halfway down (5th slot).

For the day I took the forestay down 2 additional slots (which had mast rake measurement on the top-aft hull 2" behind the port inspection lid). The helm was much better (only slight weather helm)....just wish the adjustment could correct capsize(s). <img src="http://www.catsailor.com/forums/images/graemlins/crazy.gif" alt="" />
Posted By: Jamie

Re: Measuring Mast Rake - 07/27/06 03:18 PM

Quote
In any event, it seems that my forestay is a little bit shorter than yours (presumably this is a European vs US thing).


The change that occurred is that the mast base became higher causing the forestay to be a little tight. I had to fight with mine initially to even get the forestay to the first hole. Talked to Matt because I know Robi's and Matt's are around 1 on the staymasters and I could get to maybe 7, so I knew something was different. Matt exchanged my forestay for a longer one and now I'm around the middle hole on the forestay and 4 on the staymasters. I'm carrying a lot of mast rake with the trapeze going 6 inches down the back of the transom. The boat feels good with very little weather helm. I did rake one of the rudders more forward to match the other. If I ever want to rake them back, I'll just glue in a piece of rubber. Also, my clew of my main must be cut higher as I have quick releases on both ends of the mainsheet blocks and I have yet to go block to block.

Jamie
Blade USA 714
Posted By: tback

Re: Measuring Mast Rake - 07/27/06 04:05 PM

Quote
I'm carrying a lot of mast rake with the trapeze going 6 inches down the back of the transom. The boat feels good with very little weather helm.


Holy S%*^t, That seems like alot


Quote
I did rake one of the rudders more forward to match the other.


How much forward of vertical are your rudders?
Posted By: Mark P

Re: Measuring Mast Rake - 07/27/06 06:10 PM

Call me old fashioned, or just plain stupid but I measure my mast rake between the bottom of the forestay and top of the bridle. Its very quick and easy to adjust. I also think that the new fat/square top mains don't require as much mast rake as the older designs but again I'm not a sailmaker and have no means to prove this theory. For me I just feel the boat settles in the groove quicker and for longer with minimum rake.
Posted By: scooby_simon

Re: Measuring Mast Rake - 07/27/06 08:48 PM

Quote
Call me old fashioned, or just plain stupid but I measure my mast rake between the bottom of the forestay and top of the bridle. Its very quick and easy to adjust. I also think that the new fat/square top mains don't require as much mast rake as the older designs but again I'm not a sailmaker and have no means to prove this theory. For me I just feel the boat settles in the groove quicker and for longer with minimum rake.


BUT you cannot compare that with anyone else as your wires may be of differing lengths !
Posted By: Mark P

Re: Measuring Mast Rake - 07/27/06 11:12 PM

Exactly!!!! We've previously seen that sails can't be made the same. so don't fool yourself neither are hulls, hardware, masts or rigging.
I do accept that using the trap wires is the most accurate method due to "blar, blar,blar" but lets be fair we are not Olympic Sailors.
I'm sorry I seem like a killjoy but I have yet to be convinced that Club sailors who take moor interest in boat tunning rather than boat handling win races?
Where I sail there is a F18 sailor who has digested every F18 tunning/racing guide and he is fast when he's not upside down.
Posted By: scooby_simon

Re: Measuring Mast Rake - 07/27/06 11:44 PM

Quote
Exactly!!!! We've previously seen that sails can't be made the same. so don't fool yourself neither are hulls, hardware, masts or rigging.
I do accept that using the trap wires is the most accurate method due to "blar, blar,blar" but lets be fair we are not Olympic Sailors.
I'm sorry I seem like a killjoy but I have yet to be convinced that Club sailors who take moor interest in boat tunning rather than boat handling win races?
Where I sail there is a F18 sailor who has digested every F18 tunning/racing guide and he is fast when he's not upside down.


Boats are built to a LOT higher tolerances as they would not go together otherwise, wires only need to be about right.
Posted By: Mark P

Re: Measuring Mast Rake - 07/28/06 12:22 AM

Boats are built to a LOT higher tolerances as they would not go together otherwise, wires only need to be about right. [/quote]

I see what you're getting at but I'm not convinced that the manufactures work to absoulute dead millimeter tolerances day in and day out when it comes to a fairly trivial thing such as a trap or stay wire for a beach cat.
Posted By: scooby_simon

Re: Measuring Mast Rake - 07/28/06 08:40 AM

Quote
Boats are built to a LOT higher tolerances as they would not go together otherwise, wires only need to be about right.


I see what you're getting at but I'm not convinced that the manufactures work to absoulute dead millimeter tolerances day in and day out when it comes to a fairly trivial thing such as a trap or stay wire for a beach cat. [/quote]

Excatly, so there is no point using these as the actual measuremnet menthod. Where they bi-sect the hull, YES as this is (more) constant as (having measured many boats) the trap lines are just used to provide the sides of the triangle and so need to be lengthened anyway by adding string to get to the bridal point on the hull.
Posted By: alutz

Re: Measuring Mast Rake - 07/28/06 09:50 AM

In the 18HT class, the italians measure the distance between the top and the mainsail track.

They simply pull up a long measurment tape with the mainsail halyard.
Posted By: scooby_simon

Re: Measuring Mast Rake - 07/28/06 10:23 AM

Quote
In the 18HT class, the italians measure the distance between the top and the mainsail track.

They simply pull up a long measurment tape with the mainsail halyard.


I assume you mean the traveller on the back beam.

This is another valid method, you just need a long tape measure; the "trapeze wire" method can usually be done with a bit of rope and a ruler !
Posted By: alutz

Re: Measuring Mast Rake - 07/28/06 11:51 AM

Quote

I assume you mean the traveller on the back beam.

Right!

Quote

This is another valid method, you just need a long tape measure; the "trapeze wire" method can usually be done with a bit of rope and a ruler !

I guess many ways lead to Rom <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" />
Posted By: Jamie

Re: Measuring Mast Rake - 07/28/06 01:21 PM

Quote

How much forward of vertical are your rudders?


With a yardstick against the transom and taking a point 23" below the rudder stock, the stock position had the starboard rudder at 1 7/16" forward and the port at 3/4" to 7/8" forward. With the stock settings, I had weather helm even with the short forestay and staymasters at 7-7.5. In two increments, I moved the port to 1 7/16" and at the same time of the last adjustment, moved the forestay down one hole, which took care of the tiller pull.

Jamie
Blade USA 714
Posted By: Simon

Re: Measuring Mast Rake - 07/28/06 09:57 PM

On the Spitfire we tie a rope to the trap line, pull it tight to the top of a rudder pintle, then take this forward to the foremost point where it will touch the seam on the top of the same hull. This point is measured backwards from the bridle tang. Recommended setting at 10-15 inches.

Now, I have a question - I have set my boat up the same every time since I got it 2 years ago, based on the same holes on the sidestays and then applying rig tension using the forestay. I figured if I set the boat the same all the time I could focus on sailing (rather than tuning) skills. This setting has been successful for me at club level.

Imagine my surprise then when I got home from the Spitfire Europeans, to find that rather than having somewhere between 10 and 15 inches, I had 0 / zero / none / nada / no rake whatsover by this measure. So I changed it to midway between 10 and 15 and guess what - I am convinced we were slower, actually coming second in 2 races for the first time this series!

What is going on?

Cheers
Posted By: tback

Re: Measuring Mast Rake - 07/29/06 01:15 AM

Seems to me if you rake your mast forward ... you'd have more trap line to extend back to your rudder pintle ... and consequently more trap line (and less distance to cover) to extend forward towards your bridle tang.
Posted By: JJD

Re: Measuring Mast Rake - 08/27/06 02:05 AM

Took some measurements and photos today of my setup.
The furthest forward toward vertical I can rake the mast is to get the front stay adjuster into the 8th of 10 holes. This is with the Sta/Masters slackened to the 10 mark (any further and I'd be using less than the full threads on the adjustment nut). I tensioned the rig by adjusting to 8.5 then measured the rake using the forward trapeze line.
Started at top centerline of hull in line with bridle tang.
Took this reference back to where I could touch top centerline of hull near transom. That turned out to be almost exactly 3 inches forward of the transom or about 2 inches aft of the edge of the inspection hatch ring.
Does this sound reasonable? There is no way I can go any further toward vertical unless my side stays are made longer and I shorten the forestay.
I'l attach photos in subsequent posts.
John, Blade 720 (still in drydock but closer to launch) <img src="http://www.catsailor.com/forums/images/graemlins/grin.gif" alt="" />
Posted By: JJD

Re: Measuring Mast Rake - 08/27/06 02:08 AM

Photo shows boat with maximum forward rake possible with current shrouds. Hull top is level at C/B trunk.

Attached picture 84238-Bladeprofile.jpg
Posted By: JJD

Re: Measuring Mast Rake - 08/27/06 02:24 AM

This photo show the Sta/Master fully slackened to produce previous photo.

Attached picture 84239-Sta-Masterat10.0.jpg
Posted By: JJD

Re: Measuring Mast Rake - 08/27/06 02:26 AM

This photo shows the position of the forward stay. Pin is in hole 8 of 10.

Attached picture 84240-Forestayadjustment.jpg
Posted By: bobcat

Re: Measuring Mast Rake - 08/27/06 04:54 AM

So your rake is somewhat less than mine. Put some sails on and take her for a rip. See how it feels to you.
Posted By: Anonymous

Re: Measuring Mast Rake - 08/27/06 05:01 PM

Bruce:

Do you still have the logo you sent me that says
"If it's not a Cat it's a Dog" with the bobcat with the red eyes?
If so sent it to me again. Computer crashed and I lost it.

Doug Snell
dsnell4 at houston dot rr dot com
Posted By: Wouter

Re: Measuring Mast Rake - 08/27/06 08:06 PM



It is always easy to lengthen your sidestays. Just put a shackle there (on both sides !)

It is best to have some safety margin with the staymasters. Adding two shackles will allow you that. Don't worry about the forces on the sides stays these are low enough to handled by any normal sized shackle.


Quote

Started at top centerline of hull in line with bridle tang.
Took this reference back to where I could touch top centerline of hull near transom. That turned out to be almost exactly 3 inches forward of the transom or about 2 inches aft of the edge of the inspection hatch ring.
Does this sound reasonable?


Sounds a reasonable starting point to me. Try it in that position and see how it sails/feels

Wouter
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